On 4/24/2018 2:45 PM, Steve Maki wrote:
Mostly true. For HF it's insignificant. For UHF and above it's
insignificant for receive only or simplex. For UHF duplex (repeaters)
I *think* it can be significant. LMR style cables have very poor PIM
performance (like 25 dB worse or more) compared to Heliax/hardline
style cables. I've measured PIM on LMR400 & LMR600 at 700 MHz and
above, and it's horrendous by cell service LTE standards (which is
-143 dBc using two 20 watt carriers).
Kinda surprising given that the *RF* foil shield is solid for all (or
most) practical purposes.
I suspect the issue may be degradation of the contact between the foil
and the braid. In one of the later editions of his book on Interstation
Interference, W2VJN noted significant degradation of some stubs built
with LMR400 that had been in his garage for years.
73, Jim K9YC
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